I asked them at Sonic Solutions and as of when I contacted them, they said people were running Amarra with Snow Leopard. I said i wanted to be sure before downloading Snow Leopard to be sure all the bugs were out of it for everything, esp if there ended being a problem with Amarra. He said good idea. Email them at Sonic Solutions, where you download the trial and ask. I am running regular Leopard.
By the way, I just did a short a/b with the optical out of my macpro compared to the usb and I thought the usb was much better. Got to admit though you have to go thru the hoop, you can't toggle between them. You have to close Amarra/itunes and then plug in the other connector and go to preferences and switch it, then reopen Amarra, that opens itunes and find what you were listening to. I like to toggle to do a good a/b. Anyway, I didn't like the optical as much, it wasn't even really close. Still to hear the difference between itunes and Amarra, you may be able to pick it up, I could tell more with the usb though.